1. Field of the Invention
The invention relates generally to systems for testing transducer head alignment in magnetic media data storage devices, and more particularly to systems utilizing specially prerecorded data for testing such alignment. The invention will likely have primary application to alignment of transducer heads in floppy disk drives, although application to head alignment associated with hard media including hard disks and drums is feasible.
Proper alignment of the transducer head of a magnetic data storage device, with the data tracks on the magnetic media, is essential to proper data transfer. The recent promulgation of small computers, accompanied by both integral and separate disk drives has placed ever increasing numbers of magnetic storage devices in relatively unprotected environments. The relative vulnerability to mechanical damage of inexpensive disk drives associated with home and office small computers as compared with data devices associated with large main frame computer installations is significant.
If a slight change occurs in the alignment of a transducer head of a disk drive system, that change will not affect the ability of the disk drive to reliably read data recorded on that same disk drive after such an alignment change occurred. Data recorded by a different disk drive, however, or data recorded by the same disk drive before the change in alignment occurred, may be unusable on said disk drive following such a change in alignment. A fundamental function of floppy disk data storage systems is the interfacing of data from different sources on different computers. In order to accomplish such transfer of data, it is necessary that disk drives be aligned to a common standard. The location of tracks on floppy disks is governed by ANS X3.82-1980. Although the practice as to method of formating data within those tracks varies between manufacturers, thus creating incompatibility between disks used with different manufacturers equipment, a common location of the data tracks results in a basic uniformity of floppy disk drive head alignment requirements irrespective of manufacturer.
While many methods of head alignment are possible, including complex servo systems which automatically adjust alignment, the common practice with respect to floppy disk drives has been to have head alignment consist of a manual adjustment performed by a service technician utilizing a specially recorded disk and an oscilloscope. The common "cats eye" alignment technique is described by Hersey, Jr. as background in U.S. Pat. No. 4,053,937. That technique, including various embellishments thereto such as that disclosed by the invention of Hersey, Jr. have dominated head alignment of floppy disk drives. Since such alignment requires special equipment and a qualified technician, many disk drive users relegate head alignment to the category of things generally ignored until a problem becomes apparent. Only when the problem has become severe is the disk drive taken to a service shop.
A problem which can occur involves gradual drift in disk drive head alignment. A user whose application tends toward frequent creation of new files with access frequently required of recent files and infrequently required of older files, may be totally unaware of any problem with the disk drive system even though significant head alignment drift has occurred. As long as the only data to be accessed was also recorded with the head misaligned, the misaligned head will properly read the data. Only when a disk recorded on a different disk drive or a disk recorded much earlier is accessed will there be any consequence of the head alignment shift. If the disk drive head alignment is then corrected, all of the data on recently recorded disks may thereby become inaccessible. An additional problem which can plague users is a condition where data recovery from the disk drive begins to become unreliable. It is not always easy for a user to determine the source of the problem. Malfunctions in the computer or in the disk drive controller can have symptoms similar to head misalignment.
A system by which a relatively nontechnical user can economically test the alignment of the disk drive head will allow the user both to obtain corrective action before misalignment becomes so severe as to threaten the effectiveness of data access, and to more effectively diagnose problems associated with ineffective data access.